Imaging device

ABSTRACT

An imaging device includes a plurality of first pixels that includes pixels of a plurality of color components and generates a first signal from incident light, a plurality of second pixels that generates a second signal from light that has transmitted at least a part of the first pixels, and a signal generation unit that generates a signal obtained by combining the first signal and the second signal.

PRIORITY CLAIM

This is a Continuation of U.S. application Ser. No. 15/684,474 filed onAug. 23, 2017, which is a Continuation of U.S. application Ser. No.14/903,196 filed Apr. 29, 2016, which is a National Stage Entry ofInternational Application No. PCT/JP2014/067886 filed Jul. 4, 2014,which claims the benefit of priority to Japanese Application No.2013-142761 filed Jul. 8, 2013. The disclosure of the prior applicationsare hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to an imaging device.

BACKGROUND ART

An image sensor with color filters has been known in the art (refer toPTL 1).

CITATION LIST Patent Literature

PTL1: Japanese Laid Open Patent Publication No. 2007-282109

SUMMARY OF INVENTION Technical Problem

In the conventional technology, light that has transmitted through acorresponding color filter is input into each pixel. Thus, for instance,in a G pixel that receives G (green) light, light other than the G lightis absorbed by the color filter and is not used. Furthermore, in the Gpixel not all of the G light is used; a part of the G light is absorbedor reflected by the color filter. In this manner, the conventionaltechnology has manifested a poor use efficiency of incident light.

Solution to Problem

An imaging device according to a first aspect of the present inventioncomprises: a plurality of first pixels that includes pixels of aplurality of color components and generates a first signal from incidentlight; a plurality of second pixels that generates a second signal fromlight that has transmitted at least a part of the first pixels; and asignal generation unit that generates a signal obtained by combining thefirst signal and the second signal.

According to a second aspect of the present invention, in the imagingdevice according to the first aspect, it is preferable that the firstpixels photoelectrically convert light of a specific color component outof incident light to generate the first signal and transmit light of anycolor component other than the specific color component; and the signalgeneration unit adds the first signal to the second signal to generate abrightness signal.

According to a third aspect of the present invention, in the imagingdevice according to the second aspect, it is preferable that the firstpixels include a pixel that photoelectrically converts light of a firstcolor component, a pixel that photoelectrically converts light of asecond color component, and a pixel that photoelectrically convertslight of a third color component; and the signal generation unitgenerates a color difference signal by using the first signal.

According to a fourth aspect of the present invention, it is preferablethat the imaging device according to the third aspect, it is preferablethat the signal generation unit performs color interpolation processingat a position of each pixel by using the first signal to obtain signalsof the first to the third color components, obtains image signals of thefirst to the third color components based on a ratio of the signals ofthe first to the third color components and on the brightness signal,and generates the color difference signal based on the obtained imagesignals or based on the obtained image signals and the brightnesssignal.

According to a fifth aspect of the present invention, in the imagingdevice according to the third or fourth aspect, it is preferable thatthe first color component is red, the second color component is green,and the third color component is blue; and the first pixels are arrangedin a Bayer array.

An imaging device according to a sixth aspect of the present inventioncomprises: an image sensor having a first photoelectric conversionlayer, at which pixels that photoelectrically convert light of aspecific color component of incident light and transmit light of anycolor component other than the light of the specific color component ofthe incident light are two-dimensionally arrayed, and a secondphotoelectric conversion layer arranged as stacked in a same opticalpath as that of the first photoelectric conversion layer, at whichpixels that photoelectrically convert the light that has transmittedthrough the first photoelectric conversion layer are two-dimensionallyarrayed; and an image generation unit that generates a color imagesignal by using an output signal from the first photoelectric conversionlayer and an output signal from the second photoelectric conversionlayer, wherein: the image generation unit adds the output signal fromthe first photoelectric conversion layer to the output signal from thesecond photoelectric conversion layer to generate a brightness signal inthe color image signal.

According to a seventh aspect of the present invention, in the imagingdevice according to the sixth aspect, it is preferable that the firstphotoelectric conversion layer has a first pixel that photoelectricallyconverts light of a first color component, a second pixel thatphotoelectrically converts light of a second color component, and athird pixel that photoelectrically converts light of a third colorcomponent; and the image generation unit generates a color differencesignal in the color image signal by using the output signal from thefirst photoelectric conversion layer.

According to an eighth aspect of the present invention, in the imagingdevice according to the seventh aspect, it is preferable that the imagegeneration unit performs color interpolation processing at each pixel ofthe image sensor by using the output signal from the first photoelectricconversion layer to acquire signals of the first to the third colorcomponents, acquires image signals of the first to the third colorcomponents based on a ratio of the signals of the first to the thirdcolor components and on the brightness signal, and generates the colordifference signal based on the image signals or based on the imagesignals and the brightness signal.

According to a ninth aspect of the present invention, in the imagingdevice according to the seventh or eighth aspect, it is preferable thatthe first color component is red, the second color component is green,and the third color component is blue; and the first to the third pixelsare arranged in a Bayer array.

Advantageous Effects of Invention

According to the present invention, the use efficiency of incident lightcan be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example of the arrangement ofa digital camera.

FIG. 2 is a schematic diagram illustrating an image sensor.

FIG. 3 shows diagrams illustrating an example of the arrangement ofpixels.

FIG. 4 is a diagram illustrating a method for generating a Y signal.

FIG. 5 is a diagram illustrating a method for generating Cb and Crsignals.

FIG. 6 shows diagrams illustrating an example of relative spectralresponse in an image sensor in which no color filters are arranged andin an image sensor in which color filters are arranged.

DESCRIPTION OF EMBODIMENTS

Hereafter, an embodiment of the present invention is explained withreference to the drawings. FIG. 1 is a diagram illustrating theconfiguration of a digital camera 1 according to an embodiment of thepresent invention. The digital camera 1 includes an imaging opticalsystem 10, an image sensor 11, a control unit 12, an operation unit 13,an image processing unit 14, a liquid crystal monitor 15, and a buffermemory 16. The digital camera 1 is equipped with a memory card 17.

The control unit 12, which includes a microprocessor and peripheralcircuits, executes a control program stored at a ROM (not shown infigures) to perform various types of controls of the digital camera 1.

The image sensor 11, which includes a plurality of pixels, receives alight flux from a subject via the imaging optical system 10 and performsphotoelectrical conversion to output an analog image signal or a digitalimage signal. If an analog image signal is output from the image sensor11, the analog image signal is AD-converted by an AD conversion circuit(not shown in figures) to generate a digital image signal. The digitalimage signal is store d at the buffer memory 16.

The digital image signal stored at the buffer memory 16 is subjected tovarious types of image processing at the image processing unit 14. Theresultant signal is displayed at the liquid crystal monitor 15 or storedat the memory card 17. The memory card 17 is constituted by anon-volatile flash memory or the like and is capable of being attachedto and detached from the digital camera 1.

The operation unit 13, which includes various types of operation buttonssuch as a release button, a forward-reverse button, and a power button,is operated by a photographer. The operation unit 13 outputs anoperation signal in response to the operation of each operation buttonby the photographer to the control unit 12. The image processing unit 14includes, for instance, an application specific integrated circuit(ASIC). The image processing unit 14 performs various types of imageprocessing such as interpolation, compression, and white balanceadjustment as well as the image generation processing described later onthe image data captured by the image sensor 11.

<Explanation on Image Sensor>

FIG. 2 is a schematic diagram illustrating the image sensor 11 accordingto this embodiment. FIG. 2 shows a state in which a side on which lightis incident is defined to be upside. Accordingly, in the followingexplanation, a side in which the light is incident is defined to be“upper” or “up” and a side opposite to the side in which the light isincident is defined to be “lower” or “down”. The image sensor 11 has anupper photoelectric conversion layer 31 and a lower photoelectricconversion layer 32. The upper photoelectric conversion layer 31 and thelower photoelectric conversion layer 32 are arranged as stacked one onanother in the same optical path. The upper photoelectric conversionlayer 31 is made of an organic photoelectric conversion layer thatabsorbs (photoelectrically converts) light of a specific color component(described later in detail). Light of any color component that is notabsorbed (photoelectrically converted) by the upper photoelectricconversion layer 31 transmits through the upper photoelectric conversionlayer 31 and enters the lower photoelectric conversion layer 32 to bephotoelectrically converted at the lower photoelectric conversion layer32. The lower photoelectric conversion layer 32 is made of an organicphotoelectric conversion layer that absorbs (photoelectrically converts)light having all the wavelengths of the visible light. The upperphotoelectric conversion layer 31 and the lower photoelectric conversionlayer 32 are formed on one and the same semiconductor substrate and thepositions of pixels in each layer correspond to each other one for one.For instance, the pixel at the first column in the first row of theupper photoelectric conversion layer 31 corresponds to the pixel at thefirst column in the first row of the lower photoelectric conversionlayer 32.

FIG. 3(a) is a diagram illustrating the arrangement of the pixels of theupper photoelectric conversion layer 31. In FIG. 3(a), an axis in thehorizontal direction is defined to be an x-axis and an axis in thevertical direction is defined to be a y-axis. The coordinates of a pixelP is expressed P(x, y). At the upper photoelectric conversion layer 31,the pixels are arranged, for instance, in a Bayer array. That is, asshown in FIG. 3(a), an R pixel that photoelectrically converts R (red)light and a G pixel that photoelectrically converts G (green) light arearranged alternately at an odd number row. At an even number row, a Gpixel that photoelectrically converts G (green) light and a B pixel thatphotoelectrically converts B (blue) light are arranged alternately.Light of a color component that is not photoelectrically converted(absorbed) by each pixel of the upper photoelectric conversion layer 31transmits through the upper photoelectric conversion layer 31. Forinstance, the pixel P(1, 1) of the upper photoelectric conversion layer31 absorbs and photoelectrically converts the light of R component, sothat the light of any color component other than the R componenttransmits through the upper photoelectric conversion layer 31.

FIG. 3(b) is a diagram illustrating the arrangement of the pixels of thelower photoelectric conversion layer 32. The position of each pixel asshown in FIG. 3(b) is the same as that in FIG. 3(a). For instance, thepixel P(1, 1) of the lower photoelectric conversion layer 32 correspondsto the pixel P(1, 1) of the upper photoelectric conversion layer 31. Atthe lower photoelectric conversion layer 32 are two-dimensionallyarranged pixels that are capable of absorbing light having all thewavelengths of visible light. This causes each pixel of the lowerphotoelectric conversion layer 32 to absorb and photoelectricallyconvert all the visible light that is not absorbed by the upperphotoelectric conversion layer 31 (that is, that transmits through theupper photoelectric conversion layer 31). Consequently, for instance, atthe pixel P(1,1) of the lower photoelectric conversion layer 32, thevisible light that is not absorbed at the pixel P(1, 1) of the upperphotoelectric conversion layer 31, that is, the visible light thatcontains only the color components other than the R component isabsorbed and photoelectrically converted.

<Image Generation Processing>

Now, explanation is made on image generation processing in which thesignal output from the image sensor 11 mentioned above is used togenerate a color image signal of a YCbCr format. First, explanation ismade on a method for generating a Y signal (brightness signal) withreference to FIG. 4.

As mentioned above, at the image sensor 11, each pixel of the upperphotoelectric conversion layer 31 absorbs light of one of the RGBcomponents and each corresponding pixel of the lower photoelectricconversion layer 32 receives and photoelectrically converts light of thecolor component that transmits through (i.e., is not absorbed by) theupper photoelectric conversion layer 31. As a result, addition of theoutput signal from the upper photoelectric conversion layer 31 to theoutput signal of the lower photoelectric conversion layer 32 provides asignal generated by the photoelectric conversion of the visible lightinput to the image sensor 11 without any other processing, i.e., awhite-and-black signal, which is identical with the output signal fromthe conventional image sensor provided with no color filter.

As shown in FIG. 4, the image processing unit 14 generates a Y signal(brightness signal) by adding the output signal from the upperphotoelectric conversion layer 31 to the output signal from the lowerphotoelectric conversion layer 32 at the position of each pixel. In FIG.4, r represents an output signal from an R pixel in the upperphotoelectric conversion layer 31, g represents an output signal from aG pixel in the upper photoelectric conversion layer 31, and b representsan output signal from a B pixel in the upper photoelectric conversionlayer 31. Further, w represents an output signal from a pixel arrangedat the lower photoelectric conversion layer 32, which pixel absorbs thelight having all the wavelengths of visible light. The image processingunit 14 obtains a Y signal according to the expression (1) below at theposition of an R pixel, according to the expression (2) below at theposition of a G pixel, or according to the expression (3) below at theposition of a B pixel. The image processing unit 14 normalizes the Ysignal within the range of 0 to 1.

Y=r+w  (1)

Y=g+w  (2)

Y=b+w  (3)

Now, explanation is made on a method for generating Cb and Cr signals(color difference signals) in the color image signal according to theprocess as illustrated in FIG. 5. First, the image processing unit 14performs demosaic processing (color interpolation processing) whileperforming matrix conversion for adjusting white balance or spectrum onan image signal of a Bayer array output from the upper photoelectricconversion layer 31 to obtain respective signal values of the Rcomponent, the G component, and the B component for each pixel.Hereafter, the signal of R component generated by demosaic processing isexpressed as r′ signal, the signal of G component generated by demosaicprocessing is expressed as g′ signal, and the signal of B componentgenerated by demosaic processing is expressed as b′ signal. The imageprocessing unit 14 normalizes the r′ signal, the g′ signal, and the b′signal each within the range of 0 to 1.

Then, the image processing unit 14 acquires R, and B signals as colorimage signals by using the Y signal and the r′, g′, and b′ signalsobtained by the demosaic processing. First, explanation is made onacquisition of an R signal for the color image signal. In thisembodiment, for instance, a relational expression for SDTV prescribed inITU-R BT.601 Standard as shown by the expression (4) below is used.

Y=0.299R+0.587G+0.114B  (4)

If it is assumed that the ratio of the R signal, the G signal, and the Bsignal in the color image signal is identical with the ratio of the rsignal, the g signal, and the b signal obtained by the above-mentioneddemosaic processing (that is, R:G:B=r′:g′:b′), the following expressions(5) and (6) are given.

G=(g′+r′)R  (5)

B=(b′+r′)R  (6)

Plugging in the expressions (5) and (6) for the expression (4) resultsin the following expression (7).

Y=0.299R+0.587R(g′+r′)+0.114R(b′+r′)  (7)

Transformation of the expression (7) results in the following expression(8).

R={r′÷(0.299r′+0.587g′+0.114b′)}Y  (8)

The image processing unit 14 plugs in the r′, g′, and b′ signalsgenerated by the demosaic processing and the Y signal for the expression(8) to acquire an R signal in the color image signal.

Similarly, the image processing unit 14 plugs in the r′, g′, and b′signals generated by the demosaic processing and the Y signal for thefollowing expressions (9) and (10) to acquire the G signal and B signalin the color image signal. The expressions (9) and (10) are prepared inthe same manner as that for the R signal mentioned above.

G={g′÷(0.299r′+0.587g′+0.114b′)}Y  (9)

B={b′÷(0.299r′+0.587g′+0.114b′)}Y  (10)

As mentioned above, the image processing unit 14 acquires R, and Bsignals in the color image signal by using the ratio of the r′ signal,the g′ signal and the b′ signal and the Y signal.

And the image processing unit 14 plugs in the R, and B signalscalculated according to the expressions (8) to (10) for the followingexpressions (11) and (12) to acquire a Cr signal and a Cb signal. Theexpressions (11) and (12) are relational expressions for SDTV prescribedby the ITU-R BT.601 Standard.

Cr=0.500R−0.419G−0.081B  (11)

Cb=−0.169R−0.331G+0.500B  (12)

The image processing unit 14 may be configured to plug in the Y signal,the R signal, and the B signal for the following expressions (13) and(14) to acquire a Cr signal and a Cb signal. Also, the expressions (13)and (14) are relational expressions for SDTV prescribed by the ITU-RBT.601 Standard.

Cr=0.713(R−Y)  (13)

Cb=0.564(B−Y)  (14)

As mentioned above, the image processing unit 14 uses the signals outputfrom the upper photoelectric conversion layer 31 and the output from thelower photoelectric conversion layer 32 to generate color image signalsof a YCbCr format.

According to the above-explained embodiment, the following operationsand advantageous effects can be obtained.

(1) The digital camera 1 includes the image sensor 11 having the upperphotoelectric conversion layer 31 at which pixels that photoelectricallyconvert light of a specific color component of incident light andtransmit light of any component other than the specific component of theincident light are two-dimensionally arrayed, and a lower photoelectricconversion layer 32 arranged as stacked in the same optical path as thatof the upper photoelectric conversion layer 31 at which pixels thatphotoelectrically convert light transmitted through the upperphotoelectric conversion layer 31 are two-dimensionally arrayed; and theimage processing unit 14 that generates a color image signal of a YCbCrformat by using an output signal from the upper photoelectric conversionlayer 31 and an output signal from the lower photoelectric conversionlayer 32. The image processing unit 14 adds the output signal from theupper photoelectric conversion layer 31 to the output signal from thelower photoelectric conversion layer 32 to generate a brightness signal(Y signal) in the color image signal. This enables the digital camera 1according to this embodiment to have a use efficiency of incident lighthigher than that of the conventional technology and to have a highersignal output to increase the S/N ratio of the Y signal.

For reference, FIG. 6 shows examples of relative spectral response atconventional image sensors one having no color filters and the otherhaving color filters arranged in a Bayer array. In FIG. 6, thehorizontal axis represents wavelength and the vertical axis representsoutput, with the peak output of each spectrum being normalized to 1. Forinstance, to focus on the spectrum near the wavelength of 550 nm, the Goutput from the image sensor having color filters arranged in a Bayerarray is demonstrably lower than the output from the image sensor havingno color filters. That is, at the image sensor having the color filtersarranged in a Bayer array, not all the light is used even at awavelength near the peak of G as compared with the image sensor havingno color filters. Light having wavelength different from that of G isused in a considerably decreased ratio. As mentioned above, the imagesensors having the conventional color filters manifest each a decreaseduse efficiency of light. In contrast, the digital camera 1 according tothis embodiment is capable of using the light that is otherwise absorbedby color filters in the conventional image sensors. This enables thedigital camera 1 to have a higher use efficiency of the incident lightthan that of the conventional digital camera.

(2) The image processing unit 14 in the digital camera 1 is configuredto perform demosaic processing (color interpolation processing) at eachpixel of the upper photoelectric conversion layer 31, thus generatingr′, g′, and b′ signals, to generate R, and B signals in the color imagesignal using the ratio of the r′, g′, and b′ signals and Y signal, andto generate Cb and Cr signals according to predetermined conversionformulae (expressions (11) and (12)). Unlike the conventional imagesensor in which the r′, g′, and b′ signals obtained by demosaicprocessing are used as R, and B signals in the color image signal, thisembodiment is arranged to use a Y signal to obtain R, and B signals inthe color image signal. The reason for this is as follows.

For instance, the upper photoelectric conversion layer 31 is not capableof obtaining information about the G component and the B component atthe position of the R pixel so that the respective signal values for theG component and the B component obtained by demosaic processing arevalues interpolated from the signal values of G pixel(s) and B pixel(s)near the R pixel. On the other hand, at the position of the R pixel inthe upper photoelectric conversion layer 31, the output signal from thelower photoelectric conversion layer 32 contains information about the Gcomponent and the B component. Consequently, it is expected that use ofthe output signal from the lower photoelectric conversion layer 32enables an image signal to have higher color reproducibility compared tothe image signal obtained by demosaic processing. Accordingly, thedigital camera 1 according to this embodiment is configured to use a Ysignal obtained by adding the output signal from the upper photoelectricconversion layer 31 to the output signal from the lower photoelectricconversion layer 32 to obtain R, and B signals in the color imagesignal. This enables the image signal to have color reproducibilityhigher than the conventional technology.

Variation Example 1

In the above-mentioned embodiment, explanation has been made on theexample in which the ratio of r′, g′, and b′ signals obtained byperforming demosaic processing on the output signal from the upperphotoelectric conversion layer 31 and Y signal are used to obtain R, andB signals in the color image signal and then obtain Cb and Cr signals.However, the r′, g′, and b′ signal obtained by performing demosaicprocessing on the output signal from the upper photoelectric conversionlayer 31 may be used as R, and B signals in the color image signalwithout further processing on them to generate Cb and Cr signalsaccording to the expressions (11) and (12), or according to theexpressions (13) and (14).

Variation Example 2

In the above-mentioned embodiment, explanation has been made on theexample in which the pixels are arranged in a Bayer array on the upperphotoelectric conversion layer 31. However, the arrangement of thepixels is not limited to the Bayer array. In the above-mentionedembodiment, explanation has been made on the example in which the Rpixel, the G pixel, and the B pixel are arranged in the upperphotoelectric conversion layer 31. However, the arrangement of thepixels is not limited to that used in this example. For instance, a Cypixel that receives Cy (cyan) light, an Mg pixel that receives Mg(magenta) light, and a Ye pixel that receives Ye (yellow) light may bearranged.

Variation Example 3

In the above-mentioned embodiment, explanation has been made on theexample in which the lower photoelectric conversion layer 32 is made ofan organic photoelectric conversion layer. However, the lowerphotoelectric conversion layer 32 may be made of photodiodes.

In the above description, various embodiments and variation exampleshave been explained. However, the present invention is not limited tothis. Other aspects or forms that can be conceived within the technicalconcept of the present invention are also included in the scope of thepresent invention.

The disclosure of the following priority application is hereinincorporated by reference:

Japanese Patent Application No. 2013-142761 (filed on Jul. 8, 2013)

REFERENCE SIGNS LIST

1 . . . digital camera, 10 . . . imaging optical system, 11 . . . imagesensor, 12 . . . control unit, 14 . . . image processing unit, 31 . . .upper photoelectric conversion layer, 32 . . . lower photoelectricconversion layer

What is claimed is:
 1. An imaging device, comprising: an image sensorthat comprises a first photoelectric converter that photoelectricallyconverts light having a component of a first color and generatesphotoelectric charges, a second photoelectric converter thatphotoelectrically converts light that has transmitted through the firstphotoelectric converter and generates photoelectric charges, a thirdphotoelectric converter that photoelectrically converts light having acomponent of a second color different from the first color and generatesphotoelectric charges, and a fourth photoelectric converter thatphotoelectrically converts light that has transmitted through the thirdphotoelectric converter and generates photoelectric charges; and ageneration unit that generates image data from (i) a first signal basedon the photoelectric charges generated by the first photoelectricconverter, (ii) a first addition signal obtained by adding the firstsignal to a second signal based on the photoelectric charges generatedby the second photoelectric converter, (iii) a third signal based on thephotoelectric charges generated by the third photoelectric converter,and (iv) a second addition signal obtained by adding the third signal toa fourth signal based on the photoelectric charges generated by thefourth photoelectric converter, wherein: the first and thirdphotoelectric converters are located in a first layer of the imagesensor, and the second and fourth photoelectric converters are locatedin a second layer of the image sensor that is different from the firstlayer.
 2. The imaging device according to claim 1, wherein thegeneration unit generates the image data from a signal based on thefirst signal and the first addition signal.
 3. The imaging deviceaccording to claim 1, wherein the light photoelectrically converted bythe second photoelectric converter has a component of a complementarycolor of the first color.
 4. The imaging device according to claim 1,wherein the generation unit generates the image data based on the firstaddition signal and a signal obtained by interpolating the first signalby using the third signal.
 5. The imaging device according to claim 1,wherein the generation unit generates the image data based on the firstsignal, the third signal and the second addition signal.
 6. The imagingdevice according to claim 1, wherein the generation unit generates theimage data based on the second addition signal and a signal obtained byinterpolating the third signal by using the first signal.
 7. The imagingdevice according to claim 1, wherein the light photoelectricallyconverted by the fourth photoelectric converter has a component of acomplementary color of the second color.